The present invention relates to an image recording apparatus such as a copying machine, and more particularly, to a type thereof capable of controlling light exposure amount of exposure speed in order to compensate spectral transmission characteristic of an optical filter.
In one conventional image recording apparatus, a recording medium is of transfer type recording medium such as a photosensitive sheet which comprises a microcapsule sheet (first image recording medium) and a developer sheet (second image recording medium). More specifically, in the transfer type recording mediums, the developer material is coated on a separate substrate as a separate developer or copy sheet. The first image recording medium comprises a photosensitive pressure sensitive recording medium provided with microcapsules which encapsulate therein a first material (chromogenic material or dye precursor) having first and second phases dependent on light exposure. The second image recording medium comprises the developer medium provided with a second material (developer material) which provides an output image upon reaction with the first material. The developer sheet includes a base substrate, the developer material layer and a surface resin layer. Such image recording medium is disclosed in, for example, U.S. Pat. No. 4,399,209 and Japanese Patent Application Kokai No. 58-88739.
As is well known, the image recording apparatus of this type irradiates light onto an original and a light reflected from the original or transmitted therethrough passes through an optical system such as a reflection mirror, a filter and lenses, and is focused on the photosensitive recording medium at an exposure unit. As a result, a latent image is formed on the photosensitive recording medium upon photocuring the light exposed microcapsules. Then, the light-exposed photosensitive recording medium is superposed with a developer sheet, and these sheets are pressed together at a pressure developing unit, so that non photo-cured microcapsules are ruptured to react the chromogenic material with the developer material, to thereby provide an output image on the developer sheet. After the pressure developing operation, the developer sheet is delivered to a thermal fixing unit where the output image is thermally fixed and glossy output image is obtained.
In a conventional image recording apparatus, optical filters are selectively used for reproducing a color image on the photosensitive pressure sensitive recording medium. When light passes through the filter, the light may be partily absorbed in the filter, so that optimum amount of light may not be irradiated onto the medium. In this regard, the filter must provide an idealistic spectral transmission characteristic in order to avoid light absorption in the filter.
However, such idealistic optical filter is costly. If inexpensive optical filter having low grade spectral transmission characteristic is employed, light irradiation amount to the image recording medium may be lowered, and therefore, a desirable output image may not be obtainable on the developer medium.